Sensors for determining the concentration of oxygen in a gas or a fluid find applications in a variety of fields such as environmental monitoring, food safety, and biomedical diagnostic applications. For example, environmental remediation projects often involve subsurface oxygen measurements in aqueous samples. Oxygen sensing can also be used in water quality testing as an indicator of microbial activity or presence of toxins. Similarly, oxygen sensors can be used in biomedical diagnostic applications, for example, to measure blood oxygen level. Other applications include food science, agricultural applications, surface, aquaculture, surface, storm and waste water monitoring, aerobic processes, energy exploration, production and distribution, renewable energy, transportation, fundamental research, etc.
Conventional sensors for measuring oxygen generally include electrochemical sensors. These sensors work on the principle that oxygen reduces on the surface of an electrode that is polarized at a sufficiently negative voltage. The reduction produces a current a magnitude of which is proportional to the concentration of the oxygen in a sample which is being tested (e.g., an environmental, food or biomedical sample). Such electrochemical sensors generally have to be regularly calibrated and can suffer from drift.
Furthermore conventional oxygen sensors can have a short life and can be susceptible to damage by organic solvents or hydrocarbons which can be present in the sample. For example, the field of enhanced aerobic bioremediation utilizes microorganisms already present in the soil to naturally decompose dangerous contaminants. Such contaminants can include hydrocarbons and/or organic solvents which contaminate sub-surface soil and water. Success of such bioremediation projects depend on maintaining an adequate level of dissolved oxygen in the sub-surface soil and water samples. Thus, in-situ, real time and long term measurement of dissolved oxygen in such sub-surface samples is critical in ensuring the success of enhanced bioremediation projects.